Portion of a brush



FIG. 1 is a front left perspective view of a portion of a brush showing our new design;

FIG. 2 is a right side view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a front view thereof;

FIG. 6 is a top view thereof;

FIG. 7 is a bottom view thereof; and,

FIG. 8 is a rear right perspective view thereof.

The dash-dot-dash broken lines immediately adjacent to the shaded areas represent unclaimed boundaries of the claimed design. The dotted broken lines are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a portion of a brush, as shown and described. 